Cathode with electron beam confining means

ABSTRACT

A cathode for an electron tube is described in which a plurality of coating strips of electron emissive material are distributed parallel with each other over the face of a base. Projecting means along opposite edges of each strip extend above the surface of the base and toward each other to form a gap for the passage of electrons. Also described are a method for making such a cathode, and a tool useful in performing the method of the invention.

United States Patent lnventor Alexander Bell Carlsbad, Calif.

Appl. N 0. 829,903

Filed June 3, 1969 Patented June 15, 1971 Assignee Stromberg Datagraphix, Inc. San Diego, Calif.

CATHODE WITH ELECTRON BEAM CONFINING MEANS 4 Claims, 5 Drawing Figs.

11.8. CI 313/338, 313/299, 313/309, 313/310, 313/356 Int. Cl H01] 1/00, H01 j 1/46 Field of Search 313/299,

[5 6] References Cited UNITED STATES PATENTS 2,459,841 1/1949 Rouse 313/356X 2,558,461 6/1951 Rajchman 313/299 2,932,754 4/1960 Harries et a1. 3 I 3/299X 2,977,496 3/1961 Doolittle 313/299X Primary Examiner-David Schonberg Assistant Examiner-- Paul A. Sacher Attorney-Anderson, Luedeka, Fitch, Even & Tabin ABSTRACT: A cathode for an electron tube is described in which a plurality of coating strips of electron emissive material are distributed parallel with each other over the face of a base. Projecting means along opposite edges of each strip extend above the surface of the base and toward each other to form a gap for the passage of electrons. Also described are a method for making such a cathode, and a tool useful in performing the method of the invention.

PATENTEDJUHISIQH 3,585,438

FIG.4

INVENTOR ALEXANDER BELL ATTYS CATI-IODE WITH ELECTRON BEAM CONFINING MEANS This invention relates to electron tubes and, more particularly, to a coated cathode for use in an electron tube.

Electron tubes, such as diodes and triodes, which are designed for operating at high-power levels, frequently utilize an indirectly heated cathode upon which a coating of alkaline earth carbonate is sprayed. The carbonate is relatively unstable and converts to the oxide upon heating. Coating thicknesses may range from 0.0005 to 0.0015 inch. In many cases it is preferable to provide a coating on the base metal of the cathode only where emissions are required, such as those regions which correspond to openings in a surrounding grid electrode. This permits lower grid current for a given voltage level of the grid drive, hence lower grid temperature, lower drive power, and more efficient use of the cathode emission current. The absence of coating on those portions of the cathode adjacent the grid conductors also reduces the contamination of the grid conductors by evaporated emissive materials. Known techniques for avoiding emissions from undesired cathode areas have included masking during the coating operation, and cleaning the cathode by scraping and brushing off excess coating material. Masking allows spreading of the coating material into the area where coating is not desirable if the mask does not tightly contact the cathode base, and removal of the mask fractures and flakes the edges of each coated area if the mask contacts the base. During cleaning operations, the cathode emitter coating in the areas where emissions are desired may become damaged, necessitating that the entire coating be removed and replaced. To do this, the cathode base metal has to undergo extensive chemical cleaning before the spray of alkaline earth can be successfully repeated.

It is an object of the present invention to provide an improved cathode for an electron tube.

Another object of the invention is to provide an improved method for making a cathode for an electron tube.

A further object of the invention is to provide a convenient and low cost tool for aid in practicing the method of the invention.

It is another object of the invention to provide a cathode for an electron tube which permits low grid driving power and low grid operating temperatures, which minimizes the contamination of grid conductors, and which reduces the amount of labor required in the manufacturing process.

Other objects of the invention will become apparent to those skilled in the art from the following detailed description taken in connection with the accompanying drawings wherein:

FIG; 1 is a perspective view of a cathode constructed in accordance with the invention;

FIG. 2 is a cross-sectional fragmentary view of a portion of the cathode of FIG. 1 in an intermediate manufacturing stage;

FIG. 3 is a cross-sectional fragmentary view of a portion of the cathode of FIG. 1 as completed also showing a portion ofa cooperating grid electrode;

FIG. 4 is an end view of a forming tool for use in practicing the method ofthe invention; and

FIG. Sis a sectional view taken along the line 5-5 of FIG. 4.

Very generally, the cathode of the invention comprises a base 11 having a plurality of coating strips 12 of electron emissive material thereon. The coating strips are elongated and generally parallel at spaced intervals on the surface of the base. Projecting means 13 are provided at opposite edges of each coating strip extending above the surface of the-base and toward each other to form a gap 14, for the passage of electrons, which is narrower than the coating strip.

Referring now more particularly to FIG. I the cathode of the invention in the illustrated embodiment includes a metal base 11 having a cylindrical shape. The material of which the base I] is comprised is preferably a good heat conductor and has a low vapor pressure at elevated temperatures, such as nickel or nickel alloy. As will be explained, a coating of electron emissive material is deposited on certain areas of the outer surface of the cylindrical base 11. When a filament heater is positioned within the cylindrical base, the emissive coating rises to an elevated temperature and emits free electrons as desired.

The outer surface of the base 11 is provided with projecting means comprising a plurality of elongated fins or vanes 13 extending parallel with the axis of the cylindrical base. The vanes or fins project outwardly from the outer surface of the cylindrical base, thereby defining a plurality of elongated regions between the fins. The fins may be comprised of the same material as the base, and may be cast or machined integral with the base or separately formed and suitably attached thereto. Every other elongated region of the outer cylindrical surface of the base 11 between the fins 13 is provided with a coating of electron emissive material to form the plurality of coating strips 12. The coating strips may be of any suitable material such as an alkaline earth carbonate, and of a thickness ranging from 0.0005 to 0.0015 inch, for example. Preferably, the coating material is sprayed onto the desired areas of the cathode base.

The fins 13 on opposite edges of strip 12 extend above the surface of the base and toward each other to form a gap 14 for the passage of electrons emitted by the strips. The gaps 14 extend along each strip and are narrower than the strip. The fins 13 thus serve as beam forming members, limiting the electron beam 21 emitted from each strip to the spaces between adjacent grid conductors 22. (See FIG. 3). The width of the gap is selected in accordance with the size and spacing of the grid conductors. Thus, close regulation of the width of the electron beams emitted from the various strips is attained by regulation of the width of the gap.

In practicing the method of the invention, the base 11 of the cathode is first provided with the fins 13 extending straight out from the outer surface. This may be seen in FIG. 2 in connection with a cathode of the type illustrated in FIG. 1. The coating strips 12 are then deposited on the outer surface of the cathode base by spraying on a coating of a suitable alkaline earth carbonate between every other pair of fins. Each strip may be individually sprayed with a narrow stream of material from a nozzle passed close by the cathode base, or a mask 23 adjacent but not touching the cathode base may be used in conjunction with a broad stream of sprayed material. In either method, the fins prevent the spray from depositing on the regions 16 between the strips, which are to remain uncoated. The end result is that illustrated in FIG. 2.

After the coating strips I2 -of emissive material are deposited on the base 11, the fins on opposite sides of each strip are bent toward each other to form the gaps 14. Thus, emission of electrons is closely confined in a beam in accordance with the gap width, which does not depend critically upon the width of the coating in the coating strips 12.

Because of the close regulation of the emissive region on the surface of the cathode, the drive power for the grid need not be as great in order to achieve a desired anode current. Accordingly, lower grid temperatures are also possible. Uniformity of the electron beams from the various strips is assured, in accordance with regulation of the width of the gap.

By practicing the method of the invention, the cathode construction having the aforementioned described design and advantages may be produced quickly and cheaply. The amount of labor required during manufacture is minimized over more conventional methods, since no cleaning of excess coating material off of particular regions of the cathode is required. The likelihood of damage to the coating strips during cleaning is therefore avoided, avoiding the possibility of having to pro vide extensive chemical cleaning of the base in order to repeat the spray-on operation.

Referring now to FIGS. 4 and 5, a tool for bending the fins 13 in performing the method of the invention is shown. The tool comprises an outer annular body 17 having an annular shoulder IS in the outer surface thereof near one end. The

shoulder is for convenience in attaching and locating the tool on a suitable machine, not shown. The interior of the annular tool body 17 is provided with a series of elongated ridges 19 corresponding to the positions of the uncoated portions 16 of the cathode surface. The bases of the ridges become larger in a smooth taper along their length from a minimum width to a maximum. The minimum diameter across the tops of the ridges 19 is slightly larger than the outer diameter of the cathode base 11. The effective width of the ridges, that is, the width of the ridges in the region in which they engage the tips of the fins, thereby increases along the length of the tool. The ridges have a generally trapezoidal shaped cross section and, since their effective base width increases when the cathode is drawn through the central opening of the tool, the wedgelike action of the ridges bends the fins 13 in the desired manner. Because of the gradual slope or taper of the ridges, and the gradual increase of the effective width of the ridges, the deformation takes place smoothly and continuously as the cathode is drawn through the tool. The final width and angle of the ridges corresponds to the amount of deformation desired, allowing for any partial return of the fins toward their original position.

Although described above in connection with a cathode in the shape of a circular cylinder, the cathode of the invention, and the method and the tool of the invention, may be applied in connection with cathodes of other shapes. For example, the cathode may be planar, or in the shape of a cylinder with hexagonal, elliptical, or other cross section. In any case, the position of the ridges, their distribution, and the shape of the mating surface ofthe tool body are made appropriate.

lt may therefore be seen that the invention provides an improved cathode for an electron tube. Also, the invention provides an improved method for making such a cathode, and a tool for use in performing the method of the invention. The finned cathode construction of the invention eliminates the need for cleaning of excessive spray material from the coated surface of the cathode base and provides control of electron flow from the coated areas. Lower grid drives and lower grid operating temperatures result, contamination of the grid is reduced, and the amount of labor required in manufacture is substantially reduced over previously known devices.

Various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Such modifications are intended to fall within the scope of the appended claims.

What l claim is:

1. A beam-shaping cathode for an electron tube comprising a base, a plurality of coating strips of electron emissive material on said base, said coating strips being elongated and generally parallel at spaced intervals, and projecting fins along opposite edges of each strip extending outwardly from said base at a selected acute angle to the exposed surface of said strips with the transverse gap between the upper edges of said fins being substantially less than the width of the exposed surface of said strips, said strips having thicknesses substantially less than their widths, whereby electrons emitted by said strips are confined into beams.

2. A cathode according to claim 1 wherein said base is cylindrical.

3. A cathode according to claim 1 wherein said base is cylindrical and wherein said projecting means comprise elongated fins circumferentially spaced at intervals around the outer surface of said cylindrical base.

4. A cathode according to claim 1 further including elongated grid members spaced adjacent to said cathode surface substantially out of the paths of electrons emitted from said strips. 

1. A beam-shaping cathode for an electron tube comprising a base, a plurality of coating strips of electron emissive material on said base, said coating strips being elongated and generally parallel at spaced intervals, and projecting fins along opposite edges of each strip extending outwardly from said base at a selected acute angle to the exposed surface of said strips with the transverse gap between the upper edges of said fins being substantially less than the width of the exposed surface of said strips, said strips having thicknesses substantially less than their widths, whereby electrons emitted by said strips are confined into beams.
 2. A cathode according to claim 1 wherein said base is cylindrical.
 3. A cathode according to claim 1 wherein said base is cylindrical and wherein said projecting means comprise elongated fins circumferentially spaced at intervals around the outer surface of said cylindrical base.
 4. A cathode according to claim 1 further including elongated grid members spaced adjacent to said cathode surface substantially out of the paths of electrons emitted from said strips. 